1. Field of the Invention
The invention relates to capacitive probe detection systems for providing an output signal indicative of the instantaneous capacitance of a probe located in an environment where varying environmental conditions vary the probe capacitance accordingly.
2. Description of the Prior Art
Capacitive probe detection systems are known for use in liquid level sensing systems where the capacitance of the probe varies with the level of a liquid. In such systems, a capacitive probe is excited by A.C. signals and the current flow through the probe is then amplified, rectified and filtered to provide a DC output signal which is representative of the liquid level. Such systems are generally inaccurate since a variation in liquid level not only changes the capacitance of the probe but also the resistive component. Furthermore, such systems are rendered inaccurate by spurious noise. It is known to reduce the noise factor by using screened leads but this has not been found totally satisfactory. The use of screened leads adds to the complexity of the system and therefore to the cost.
It is an object of the invention to provide an improved capacitive probe detection system.
It is a more specific object to provide a capacitive probe detection system which minimizes the effect of noise and the resistive component of the probe to provide a more accurate detection system.